Actually, from what I've read it sounds as if NCL has moderated their position to some extent, since their original release. Of course, we won't know how they'll actually enforce it until next year, but it sounds like if you make a specific complaint (emphasis on the word "specific" -- rather than "I just don't think it was good enough") against a specific service-worker, they may refund a portion of the charge.
That sounds like a great compromise to me. It gives passengers a release-valve: They cannot claim that the amount of service charge is out of their control completely. More importantly, it would provide two benefits to the system: (1) a validation step so that people aren't able to remove or reduce the charge out of stinginess; and (2) a rich source of first-hand information about actual service performance of specific service-workers.